Rfid uhf stripline antenna-coupler

ABSTRACT

A system having a multi-coupler array is provided. Each coupler is configured to communicate with a targeted transponder from among a group of multiple adjacent transponders. The couplers may each include one or more conductive strips, at least one terminating load, a dielectric material, a first ground plane, and a second ground plane. Each of the conductive strips can extend between the first and second ground planes and the dielectric material from an input end connected to a transceiver to a loaded end connected to the terminating load. The conductive strips may be configured to propagate electromagnetic fields concentrated in a near field region of the conductive strips in a direction generally perpendicular to the conductive strips to couple with a targeted transponder. The coupler may include an enclosure for directing the electromagnetic fields. The conductive strip may have a tapered or non-linear profile such as a modified bow-tie profile.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 11/829,455, filed on 27 Jul. 2007, which is acontinuation-in-part application of U.S. patent application Ser. No.11/371,785, filed on 9 Mar. 2006 (now U.S. Pat. No. 7,586,410, issued 8Sep. 2009), both of which are incorporated herein by reference in theirentireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention.

The present invention relates to RFID antenna-couplers and, inparticularly, to spatially selective antenna-couplers capable ofselectively communicating with a targeted transponder from among a groupof adjacent transponders.

2. Description of Related Art.

Radio frequency identification (RFID) transponders, either active orpassive, are typically used with an RFID transceiver or similar devicefor communicating information back and forth. In order to communicate,the transceiver exposes the transponder to a radio frequency (RF)electromagnetic field or signal. In the case of a passive transponder,the RF electromagnetic field energizes the transponder and therebyprompts the transponder to respond to the transceiver by re-radiatingthe received signal back and modulating the field in a well-knowntechnique called backscattering. In the case of an active transponder,the transponder may respond to the electromagnetic field by transmittingan independently powered reply signal to the transceiver.

Problems can occur when interrogating multiple adjacent transpondersregardless on whether the transponders are passively or activelypowered. For example, an interrogating electromagnetic signal mayactivate more than one transponder at a given time. This simultaneousactivation of multiple transponders may lead to collision orcommunication, i.e. read and write, errors because each of the multipletransponders may transmit reply signals to the transceiver at the sametime.

Several collision management techniques commercially exist for allowingnear simultaneous communication between multiple transponders and asingle transceiver while reducing communication errors. However, suchcollision management techniques tend to increase system complexity,cost, and delay response. Furthermore, such techniques are often “blind”in that they cannot locate a given transponder or more specificallyrecognize the position of a transponder within the interrogating RFelectromagnetic field. For example, in a printer-encoder device, thedevice would not know whether the transceiver was communicating with atransponder proximate to the printhead or not.

Another method of preventing multiple transponder activation is toelectrically isolate transponders from one another. For example, devicesor systems may employ an RF-shielded housing or anechoic chamber forshielding the adjacent and non-targeted transponders from theelectromagnetic field. In various applications, transpondersindividually pass though a shielded housing for individualized exposureto an interrogating RF electromagnetic field. Unfortunately, RE-shieldedhousings add cost and complexity to a system and limit the type (i.e.,size) of transponders that can be processed by the system. Furthermore,many systems are limited with regard to space or weight and, thus,cannot accommodate such shielded housings.

The challenge of avoiding multiple transponder activation may beespecially acute in some applications. RFID printer-encoders are oneexample. RFID printer-encoders are devices capable of encoding andprinting on a series or stream of labels with embedded transponders. Theclose proximity of the transponders to each other, during processing,makes targeting a particular transponder for encoding purposesproblematic. Moreover, the space, cost, and weight restrictionsassociated with such devices, among other factors, make collisionmanagement techniques or shielding components for alleviating multipletransponder activation less than desirable.

In light of the foregoing it would be desirable to provide a RFID systemor device capable of interrogating individual transponders positionedamong multiple adjacent transponders without the need for collisionmanagement techniques or shielding components.

BRIEF SUMMARY

The present invention may address some of the above needs by providing astripline antenna-coupler for a RFID system configured to selectivelycommunicate with a targeted transponder from among a group of multipleadjacent transponders. The antenna-coupler is adapted to have acontrolled transmission range that can be limited to minimize theinadvertent activation of transponders outside a transponder encodingregion. As such, the antenna-coupler operates with little to noanti-collision management techniques or shielding components. Theantenna-coupler of the present invention is relatively compact with alength usually one-half wavelength or less minimizing the footprint ofthe antenna-coupler within the space-restricted RFID system. Also, theantenna-coupler may have an enclosure configured to encourage aparticular direction or profile of the transmission signals of theantenna-coupler. For example, the antenna-coupler may be configured forside coupling, i.e. the antenna-coupler may be perpendicular to thetargeted transponder, which may be beneficial in a variety ofspace-restricted systems.

According to one embodiment of the present invention, the RFID systemmay include a transponder conveyance and an antenna-coupler. Thetransponder conveyance is adapted to transport the targeted transponderthrough the transponder encoding region along a predetermined path. Theantenna-coupler may be a near field antenna-coupler and be configured tocouple with the targeted transponder in the transponder encoding region.And the antenna-coupler may be perpendicular to the targeted transponderduring coupling. The system may further include a transceiver that is inelectrical communication with the antenna-coupler. The transceiver isconfigured to generate communication signals.

The antenna-coupler may include a first ground plane and a second groundplane spaced apart from each other and connected by one or moreconnections and at least two conductive strips positioned between theground planes. The conductive strips are configured to propagate aplurality of electromagnetic fields, while the ground planes andconnections between them are configured to promote the propagation ofthe electromagnetic fields from a side of the conductive strips. Morespecifically, the electromagnetic fields from the side of the conductivestrips may be in a direction generally perpendicular to the length ofthe conductive strips and generally parallel to the grounds planes forcoupling with the targeted transponder in the transponder encodingregion. For example, the near field antenna-coupler may include a numberof connections that extend substantially around the conductive stripsand define one active side of the antenna-coupler free of connectionsand is configured to promote the propagation of the electromagneticfields from the active side for coupling with the targeted transponder.

The antenna-coupler may also have a dielectric material positionedbetween the first ground plane and the second ground plane. For example,the dielectric material may be FR4 or air.

The antenna-coupler may also include an input port for connecting theantenna-coupler to the transceiver and at least one terminating load.Each of the conductive strips may extend from a first end that isconnected to the input port and a second end that is connected to the atleast one terminating load. Each second end of each conductive strip maybe terminated by an individual terminating load (i.e., one load perstrip) such that the load impedance (“Z_(L)”) equals the input impedance(“Z_(IN)”) multiplied by the number of conductive strips of theantenna-coupler (“N”). Alternatively, the second ends of the conductivestrips may be terminated by a common terminating load (i.e., theconductive strips are terminated by the same load) such that Z_(L)equals Z_(IN).

The antenna-coupler of the present invention may further be configuredto operate within a band of frequencies. Each conductive strip defines awidth and a length. According to one embodiment of the presentinvention, the width of a conductive strip remains substantiallyconstant and the length of the conductive strip is substantially equalto one half wavelength of the centered frequency within the band offrequencies. According to another embodiment, the width of theconductive strip varies forming a tapered profile and the length of theconductive strip is equal to or less than one half wavelength of thecentered frequency. For example, the tapered profile of a conductivestrip may be a modified bow-tie profile, an exponential profile, atriangular profile, a Klopfenstein profile, and a Hecken profile.

The dielectric material may form a number of dielectric substratesdepending on the number of conductive strips. A conductive strip may bedirectly deposited onto one of the surfaces of the dielectricsubstrates. Or the dielectric material may form one overall substratelayer having cut-outs for receiving the conductive strips.

According to one embodiment of the present invention, the input port isadjacent to one of the ground planes and is connected to the first endof each of the conductive strips by a connection extending through theground plane, the dielectric material, and to the conductive strips.

The antenna-coupler may have a first and a second terminating load. Thefirst terminating load may be adjacent to the first ground plane and maybe connected to the second end of the first conductive strip by aconnection extending through the first ground plane, the dielectricmaterial, and to the first conductive strip. The second terminating loadmay be adjacent to the second ground plane and is connected to thesecond end of the second conductive strip by a connection extendingthrough the second ground plane, the dielectric material, and to thesecond conductive strip. Alternatively, each of the terminating loadsmay be on the same ground plane. Each connection may be a via, such as ahidden or buried via.

Each of the conductive strip defines a characteristic impedance whichmay be less than the load impedance. For example, the load impedance maybe substantially equal to 50 ohms and the characteristic impedance maybe less than 50 ohms.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a side schematic view of a printer-encoder according to anembodiment of the present invention;

FIG. 2A is a simplified cut-away top view of a web of media unitspassing over an antenna-coupler according to an embodiment of thepresent invention;

FIG. 2B a cross-section view of the web and antenna-coupler of FIG. 2A;

FIG. 3 is a perspective view of an electro-magnetic field distributionof the antenna-coupler of-FIG. 2B;

FIG. 4 is a simplified cut-away bottom view of a web of media unitspassing over an antenna-coupler array according to another embodiment ofthe present invention;

FIG. 5 is a simplified cut-away bottom view of a web of media unitspassing over an antenna-coupler array according to yet anotherembodiment of the present invention;

FIG. 6A is a cross-sectional side view of an antenna-coupler accordingto another embodiment of the present invention; and

FIG. 6B is a perspective exploded view of the antenna-coupler of FIG.6A.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the invention is shown. Indeed, this invention may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

The present invention concerns an apparatus for enabling an RFIDtransceiver (sometimes referred to as a “reader”) to selectivelycommunicate with a targeted transponder that is commingled among orpositioned in proximity to multiple adjacent transponders. As will beapparent to one of ordinary skill in the art, various embodiments of thepresent invention are described below that selectively communicate witha targeted transponder requiring little to no physical isolation of thetransponder using space-consuming shielded housings, anechoic chambers,or relatively more complex or costly collision management techniques.

Several embodiments of the present invention may be useful for reading,writing, or otherwise encoding passive or active transponders located onassembly lines, in inventory management centers where on-demand RFIDlabeling may be needed, or in other similar circumstances, where thetransponders are in close proximity to each other. In variousembodiments, one or more transponders are mounted to or embedded withina label, ticket, card, or other media form that may be carried on aliner or carrier. In alternate linerless embodiments, a liner or carriermay not be needed. Such RFID enabled labels, tickets, tags, and othermedia forms are referred to collectively herein as “media units.” Aswill be apparent to one of ordinary skill in the art, it may bedesirable to print indicia such as text, numbers, barcodes, graphics,etc., to such media units before, after, or during communications withtheir corresponding transponders.

The present invention has been depicted, for illustration purposes, inthe context of a specific application, namely, RFID enabled printersystems, also referred to herein as “printer-encoders.” Examples ofprinter-encoders are disclosed in commonly-owned U.S. Pat. Nos.6,481,907 and 6,848,616, which are hereby incorporated herein byreference. However, the inventive concepts described herein are notlimited to printer-encoders and may be applied to other RFID enabledsystems that may benefit from the ability to selectively communicatewith a targeted transponder disposed among multiple adjacenttransponders close to the antenna-coupler.

FIG. 1 illustrates an RFID printer-encoder 20 structured for printingand programming a series or stream of media units 24 according to oneembodiment of the present invention. In various embodiments, as shown inFIGS. 2A and 2B, at least a few of the media units 24 includetransponders 26. As noted above, media units may include labels, cards,etc, that are carried by a substrate liner or web 22 as shown.

Referring back to FIG. 1, the printer-encoder 20 includes severalcomponents, such as a printhead 28, a platen roller 29, a feed path 30,a peeler bar 32, a media exit path 34, rollers 36, a carrier exit path38, a take-up spool 40, a ribbon supply roll 41, a transceiver 42, acontroller 45, and an antenna-coupler 50. The web 22 is directed alongthe feed path 30 and between the printhead 28 and the platen roller 29for printing indicia onto the media units 24. The ribbon supply roll 41provides a thermal ribbon (not shown for clarity) that extends along apath such that a portion of the ribbon is positioned between theprinthead 28 and the media units 24. The printhead 28 heats up andpresses a portion of the ribbon onto the media units 24 to printindicia. The take-up spool 40 is configured to receive and spool theused ribbon. This printing technique is commonly referred to as athermal transfer printing. However, several other printing techniquesmay be used including, but not limited to, direct thermal printing,inkjet printing, dot matrix printing, and electro-photographic printing.

After printing, as shown in FIG. 1, the media unit web 22 proceeds tothe media exit path 34 where the media units are typically individuallyremoved from the web 22. For example, in one embodiment, pre-cut mediaunits 24 may be simply peeled from the web 22 using the peeler bar 32 asshown. In other embodiments, a group of multiple media units may bepeeled together and transmitted downstream to an in-line cutter forsubsequent separation (not shown). Various other known media unitremoval techniques may be used as will be apparent to one of ordinaryskill in the art.

In applications, such as the depicted embodiment, in which the mediaunits 24 are supported by a web 22, the web 22 may be guided out of theprinter-encoder 20 along the carrier exit path 38 by rollers 36 or otherdevices. Techniques and structures for conveying or guiding the web ofmedia units along the entire feed path of the printer-encoder are wellknown in the art and, thus, such techniques and conveyance systems arenot described in great detail.

The transceiver 42 is configured for generating and transmitting RFcommunication signals that are broadcasted by the spatially selectiveantenna-coupler 50 located proximate the media feed path 30. Forpurposes of the present specification, the transceiver 42 and theantenna-coupler 50 may be referred to collectively as forming at leastpart of a communication system. As will be explained in more detailbelow, the communication system transmits an electromagnetic signal orpattern for establishing, at predetermined transceiver power levels, amutual coupling between the transceiver and a targeted transponder of amedia unit that is located in the transponder encoding region, such thatdata may be read from and written to transponder. The electromagneticsignal has a far field component and a near field component. In general,the far field component is too weak to activate or communicate with anyof the transponders, while the near field component is concentratedmostly in the transponder encoding region such that it only activates orcommunicates with the transponders in the transponder encoding region.

In general, the transceiver is a device configured to generate, process,and receive electrical communication signals. One in the art wouldappreciate that similar devices such as transmitters, receivers, ortransmitter-receivers may be used within this invention. “Transceiver”as used in the present application and the appended claims refers to thedevices noted above and to any device capable of generating, processing,or receiving electrical and/or electromagnetic signals.

FIG. 3 illustrates the stripline antenna-coupler 50 in accordance withan embodiment of the present invention. The antenna-coupler 50 isstructured in electrical communication with the transceiver (not shownin FIG. 3) for receiving and broadcasting the signals originating fromthe transceiver to the targeted transponder. In the depicted embodiment,the stripline antenna-coupler 50 includes a first ground plane 52, afirst dielectric substrate 54, a conductive strip 56, a seconddielectric substrate 58, a second ground plane 60, an input port 62 anda terminating load 64.

The ground planes 52, 60, the dielectric substrates 54, 58, and theconductive strip 56 are stacked such that the conductive strip 56 isbetween the dielectric substrates 54, 58 and the ground planes 52, 60.More specifically, according to the illustrated embodiment of FIG. 3,the first ground plane 52 has a first surface and an opposite secondsurface. The first dielectric substrate 54 has a first surface and anopposite second surface. The first surface of the first dielectricsubstrate 54 is adjacent to the second surface of the first ground plane52. The conductive strip 56 also has a first surface and an oppositesecond surface. The first surface of the conductive strip 56 is adjacentto the second surface of the first dielectric substrate 54. The seconddielectric substrate 58 has a first surface and an opposite secondsurface. The first surface of the second dielectric substrate 58 facesthe second surface of the first dielectric substrate 54 and is adjacentto the second surface of the conductive strip 56. The second groundplane 60 has a first surface and an opposite second surface. The firstsurface of the second ground plane 60 is adjacent to the second surfaceof the second dielectric substrate 58.

Although the first and second dielectric substrates 54, 58 are primarilydescribed as separate layers within the antenna-coupler 50, the firstand second dielectric substrates may be one overall substrate ordielectric layer that is between the two ground planes 52, 60 andincludes a cut-out area configured to receive the conductive strip 56.Also, the ground planes and dielectric substrates are depicted as beinggenerally rectangular in shape. However, the general shape of the groundplanes and the dielectric substrates may vary between applications. Forexample, the ground planes and the dielectric substrates may be aportion of a relatively larger printed circuit board. The dielectricsubstrates may be made or constructed from various dielectric materials,including but not limited to, plastics, glasses, ceramics, orcombinations such as Rogers materials, Isola materials, or woven glassreinforced epoxy laminate, commonly referred to as “FR4” or flameresistant 4. Moreover, the dielectric material may be air. Therefore thetwo ground planes may be spaced apart from each other and have only airand the conductive strip between them. One in the art would appreciatethat these various materials may be used to achieve a specificdielectric constant.

FIGS. 6A and 6B illustrate the stripline antenna-coupler 150 inaccordance with another embodiment of the present invention. Rather thanhaving one conductive strip, the stripline antenna-coupler 150 may havemultiple conductive strips. For example, according to the embodiment ofFIG. 6A, the stripline antenna-coupler 150 has two conductive strips156, 157. In this depicted embodiment, the stripline antenna-coupler 150includes a first ground plane 152, a first dielectric substrate 154, afirst conductive strip 156, a second dielectric substrate 158, a secondground plane 160, a second conductive strip 157, a third dielectricsubstrate 159, an input port 162 and first and second terminating loads164, 165.

The ground planes 152, 160, the dielectric substrates 154, 158, 159 andthe conductive strips 156, 157 are stacked such that the conductivestrips 156, 157 are between the dielectric substrates 154, 158, 159 andthe ground planes 152, 160. More specifically according to theillustrated embodiment of FIGS. 6A and 6B, the first ground plane 152has a first surface and an opposite second surface. The first dielectricsubstrate 154 has a first surface and an opposite second surface. Thefirst surface of the first dielectric substrate 154 is adjacent to thesecond surface of the first ground plane 152. The first conductive strip156 also has a first surface and an opposite second surface. The firstsurface of the first conductive strip 156 is adjacent to the secondsurface of the first dielectric substrate 154. The second dielectricsubstrate 158 has a first surface and an opposite second surface. Thefirst surface of the second dielectric substrate 158 faces the secondsurface of the first dielectric substrate 154 and is adjacent to thesecond surface of the first conductive strip 156. The second conductivestrip 157 has a first surface and an opposite second surface. The firstsurface of the second conductive strip 157 faces the second surface ofthe second dielectric substrate 158 and is adjacent to the secondsurface of the second dielectric substrate 158. The third dielectricsubstrate 159 has a first surface and an opposite second surface. Thefirst surface of the third dielectric substrate 159 faces the secondsurface of the second conductive strip 157 and is adjacent to the secondsurface of the second conductive strip 158. The second ground plane 160has a first surface and an opposite second surface. The first surface ofthe second ground plane 160 is adjacent to the second surface of thethird dielectric substrate 159.

Although the first, second, and third dielectric substrates 154, 158,159 are primarily described as separate layers within theantenna-coupler 150, the first, second, and third dielectric substratesmay be one overall substrate or dielectric layer that is between the twoground planes 152, 160 and includes cut-out areas configured to receivethe conductive strips 156, 157. Also, the ground planes and dielectricsubstrates are depicted as being generally rectangular in shape.However, the general shape of the ground planes and the dielectricsubstrates may vary between applications. For example, the ground planesand the dielectric substrates may be a portion of a relatively largerprinted circuit board. The dielectric substrates may be made orconstructed from various dielectric materials, including but not limitedto, plastics, glasses, ceramics, or combinations such as Rogersmaterials, Isola materials, or woven glass reinforced epoxy laminate,commonly referred to as “FR4” or flame resistant 4. Moreover, thedielectric material may be air. Therefore the two ground planes may bespaced apart from each other and have only air and the conductive stripbetween them. One in the art would appreciate that these variousmaterials may be used to achieve a specific dielectric constant.

As an example only, the stripline antenna-coupler 50 having a singleconductive strip as in FIG. 3 may have approximately the followingoverall dimensions 3.5×18×100 mm and the stripline antenna-coupler 150having two conductive strips as in FIG. 6A may have approximately thefollowing overall dimensions 6×14×100 mm. The bow-tie shaped conductivestrip may have a width that varies linearly from 9 mm to 4.5 mm back to9 mm. For the double conductive strips, each conductive strip may have awidth that varies linearly from 10 mm to 3 mm back to 10 mm. The linearlength of the conductive strip (from end to end) may be approximately 64mm in an embodiment having a single conductive strip. The linear lengthof the conductive strip (from end to end) may be approximately 57 mm inan embodiment having two conductive strips.

As explained in more detail below, the conductive strip 56 (or strips156, 157) provides a conductive plane for the propagation ofelectromagnetic waves from the antenna-coupler to a targetedtransponder. The conductive strip is fabricated from a conductivematerial. For example only, the conductive material may be copper, gold,silver, aluminum or combination thereof, or doped silicon or germanium.The conductive strip 56 has a length extending from a first end,referred to herein as the input end 66, to a second end, referred toherein as the loaded end 68. The conductive strip 56 defines a widthfrom a first side edge 70 to a second side edge 72. The conductive strip56 also has a thickness extending from the first surface of theconductive strip to the second surface of the conductive strip.

The method of fabricating the antenna-coupler, including the conductivestrip may vary. For example and as noted above, the dielectric substratemay include a cut out area in which the conductive strip is insertedinto. The conductive strip may also be deposited directly onto eitherthe second surface of the first dielectric substrate or the firstsurface of the second dielectric substrate. For example only, theconductive strip may be printed or etched onto one of these surfaces.

The input end 66 of each conductive strip is connected to the input port62. For example only and as shown in FIG. 3, the input port 62 may beadjacent to the first surface of the first ground plane 52 and may beconnected to the input end 66 of the conductive strip by a vias or otherconnection 74 extending through the first ground plane 52 and the firstdielectric substrate 54 to the conductive strip 56. For the embodimentof FIG. 6A, the input port 162 may be connected to both the input endsof the first and second conductive strips 156, 157 by a via or otherconnection 174 extending through the first ground plane 152 andextending through the dielectric substrates 154, 158 to the conductivestrips 156, 157.

Referring back to FIG. 3, the loaded end 68 of the conductive strip isconnected to the terminating load 64. The terminating load 64 may beadjacent to the first surface of the first ground plane 52 and may beconnected to the loaded end 68 of the conductive strip by a via or otherconnection 76 extending through the first ground plane 52 and the firstdielectric substrate 54 to the conductive strip 56. As another example,in the embodiment illustrated in FIG. 6A, each of the loaded ends 168,169 of the first and second conductive strips 156, 157 may be connectedto a terminating load 164, 165 by one or more vias or other connections176, 177. Although depicted as two separate terminating loads 164, 165,in other embodiments each loaded end 168, 169 may be connected to thesame terminating load.

The input port 62 connects the transceiver directly (or indirectlythrough any form of transmission line) to the antenna-coupler. Forexample, the input port may be a “RF port” as known in the art. Inparticular, the transceiver is configured to send an electrical sourcesignal to the antenna-coupler through the input port. The signal passesthrough the input port 62, the conductive strip 56, and into theterminating load 64, which is connected to at least one of the groundplanes 52, 60.

In general as the electrical signal passes through a conductive strip,the conductive strip operates as a transmission line, rather thanoperating as a standing wave radiating antenna or magnetic fieldgenerating coil. The passing signal in the conductive strip generateselectromagnetic fields concentrated in the near field region of theconductive strip. The electromagnetic fields may be adapted to couplethe antenna-coupler to a transponder disposed proximate the conductivestrip, referred to herein as the transponder encoding region. A moredetailed description of the electromagnetic fields concentrated in thenear field region, also known as “leaky” electromagnetic fields, isprovided in “Leaky Fields on Microstrip” L. O. McMillian et al. Progressin Electromagnetics Research, PIER 17, 323-337, 1997 and in commonlyowned U.S. Patent Application Publication Nos. 2005/0045723 and2005/0045724 to Tsirline et al., which are hereby incorporated byreference. The effective range of antenna-couplers relying on such leakyelectromagnetic fields is limited because the fields degrade, at anexponential rate, with increasing distance from the antenna-coupler.This limited range reduces the likelihood that a given transceiver'ssignal will activate transponders outside the transponder encodingregion.

As stated above the conductive strip is terminated at one end by theterminating load. The terminating load is configured to have animpedance value substantially equal to a source impedance defined by thetransceiver and its related circuitry. For example, the terminating loadand the source impedance may be 50 ohms. In general, at the centeroperating frequency, the input impedance of the antenna-coupler measuredat the input end of a conductive strip that has a linear length (i.e.,measured from the input end to the loaded end) of one half wavelength,or multiple thereof, is substantially equal to the terminating loadregardless of the characteristic impedance of the conductive strip. Alinear conductive strip (i.e., a conductive strip have a constant width)may be effectively shortened by tapering the conductive strip, such thatthe width of the conductive strip varies over the length of theconductive strip. In other words, a tapered conductive strip having alength less than one half wavelength is similar to a conductive striphaving a length equal to one half wavelength in that it has minimalimpact on the input impedance. The characteristic impedance of theconductive strip is defined by the width of the conductive strip.Because it has no or minimal influence on the input impedance of theantenna-coupler at the center operating frequency, the conductive stripis dimensioned to achieve proper coupling with a targeted transponder,while the terminating load is configured to maintain an impedance matchbetween the antenna-coupler and the transceiver. For example, the widthof the conductive strip may be decreased or increased at selective areasto produce a desired operating bandwidth of the antenna-coupler.Decreasing the width of the conductive strip at its center generallyincreases (i.e. widens) the bandwidth.

Although the relationship between the characteristic impedance of theconductive strip and the terminating load impedance may vary, accordingto one embodiment the characteristic impedance is less than theterminating load impedance. Terminating the conductive strip with aterminating load allows for impedance matching. Further, terminating theconductive strip with a terminating load that is substantially equal tothe source impedance and greater than the characteristic impedance ofthe conductive strip forms what is known in the art as a “band-passfilter.” A band-pass filter is a device that is configured to transmitsignals in a particular frequency band or bandwidth. For example, theantenna-coupler may have an operating frequency band of 902 MHz-928 MHzand a center operating frequency of 915 MHz.

FIGS. 2B and 3 illustrate one example of a tapered conductive strip 56according to an embodiment of the present invention. One side edge 72 ofthe conductive strip is angled inwardly from the input end 66 to amidpoint in the conductive strip 56 then the side edge 72 is angledoutwardly from the midpoint to the loaded end 68. The opposite side edge70 of the conductive strip remains substantially straight and parallelrelative to the length of the conductive strip 56 from the input end 66to the loaded end 68. The two side edges 70, 72 together define a“modified bow-tie” profile. However the profile of the conductive stripmay vary. One in the art would appreciate the various possible taperedprofiles including, but not limited to, exponential, triangular,Klopfenstein, and Hecken taper profiles.

In embodiments having more than one conductive strip, a wider operatingbandwidth may be achieved by varying the lengths of the individualconductive strips. More specifically, in an embodiment have first andsecond conductive strips, a length of the first conductive strip may beshorter and a length of the second conductive strip may be longer thanthe resonating length (e.g., ¼, and ½ wavelengths) of the conductivestrips. In an embodiment having a first conductive strip, a secondconductive strip, and a third conductive strip, a length of the firstconductive strip me be shorter, a length of the second conductive strip(between the first and third conductive strips) may be substantiallyequal to, and a length of the third conductive strip may be longer thanthe resonating length of the conductive strips. By varying the lengths,the antenna-coupler has a wider operating bandwidth compared to anembodiment in which the conductive strips have the same length relativeto one another.

One aspect of the present invention is the orientation of theantenna-coupler and, more particularly, of the conductive strip to thetargeted transponder during coupling. As illustrated in FIG. 3, thedielectric substrates 54, 58 adjacent to the first and second surfacesof the conductive strip 56 along with the ground planes 52, 60 promotethe propagation of the electromagnetic fields E, H from the side edges70, 72 of the conductive strip in a direction generally perpendicular tothe length of the conductive strip 56 and generally parallel to theground planes 52, 60 (referred to herein as side propagation) and thusfacilitates the coupling with a transponder that is positioned generallyperpendicular to the conductive strip 56 and thus the antenna-coupler(referred to herein as side coupling). As used herein, the transponderand antenna-coupler are considered to be perpendicular when the width ofthe conductive strip is perpendicular to a length of the transponder.

To further promote side propagation, the two ground planes 52, 60 may beconnected along their perimeters, such that the two ground planes 52, 60are connected along three sides. The fourth and unconnected side isreferred to as the active side 78. The ground planes 52, 60 in effectform an envelope or an enclosure for receiving the conductive strip 56,where one side, i.e., the active side 78, of the envelope is opened suchthat the electromagnetic fields propagate out of the envelope and aredirected or aimed at the targeted transponder. For example and as shownin FIGS. 2B and 3, the two ground planes 52, 60 may be connected by aseries of vias 80 extending along the three sides. Also, as shown, inthe modified bow-tie profile embodiment, the substantially straight sideedge 70 of the conductive strip 56 is positioned such that it is facingout and near the active side 78 defined by the ground planes 52, 60. Theconnected sides of the ground planes 52, 60 will further promote sidepropagation from the straight side edge 70 of the conductive stripthrough the active side 78 defined by the ground planes 52, 60. Whilethe described embodiment uses a plurality of vias 80 to connect thefirst and the second ground planes 52, 60, a plurality of vias is onlyan example of the type of connections that may be employed with thepresent invention. Another example includes using additional groundplanes or combination of additional ground planes and vias to connectthe first and second ground planes along their edges to create theenvelope for receiving the conductive strip. Creating an envelope asdescribed herein (e.g., stitching three sides of the antenna-couplerwith vias or other connections) is also applicable for multipleconductive strip embodiments, such as the embodiment illustrated in FIG.6A.

In yet another means of promoting side propagation may be the shape ofthe conductive strip. For example, the modified bow-tie profile of theillustrated embodiment, concentrates a maximum magnetic field strength Hat the straight side edge 70 near the middle point where the width ofthe conductive strip 56 is the narrowest, as well as fringe electricfields E along the side edge 70.

As illustrated in FIGS. 2A and 2B, the enclosed design of theantenna-coupler 50 also provides a novel architecture for theprinter-encoder installation. Also described above, within a printerencoder, a web 22 of media units 24 may be directed along a feed path 30by a media conveyance system. The feed path includes passing near orthrough the transponder encoding region where the antenna-coupler isconfigured to couple with the transponders of the media units. Thedirection of the feed path near or through the transponder encodingregion defines a feed direction. Because the antenna-coupler of thepresent invention is configured for side coupling, the antenna-coupler50 may be generally perpendicular to the web 22 of media units 24. Asused herein, an antenna-coupler is generally perpendicular to the web ofmedia units when the width of the conductive strip, which also generallydefines a width of the antenna-coupler, is generally perpendicular tothe feed direction.

This configuration of the antenna-coupler in a generally perpendicularorientation relative to the feed path may provide a desiredprinter-encoder architecture, structure, or configuration. Specifically,because the width of the antenna-coupler is relatively vertical, theantenna-coupler occupies less horizontal space in the printer-encoderproviding more horizontal space or allowing for a more horizontallycompact package, which in turn allows for smaller media unit sizes.

Although the present invention has been primarily described as anantenna-coupler for an RFID enabled system, the present invention mayemploy more than one antenna-coupler. For example and as shown in FIG.4, the present invention may include more than one antenna-coupler 50.The antenna-couplers 50 together define an antenna-coupler array.Individual antenna-couplers within the array may be selectivelyactivated in order to follow a targeted transponder as it moves along apredetermined path within the system or accommodate different size ortype of tags.

The orientation of the antenna-couplers 50 to the feed path 30 or toeach other may vary. As shown in FIG. 4, the antenna-couplers 50 may besubstantially parallel to each other and generally perpendicular to thefeed path 30. FIG. 5 illustrates another embodiment of anantenna-coupler array having at least one antenna-coupler 50 a that isperpendicular to the feed path and at least one other antenna-coupler 50b that is at a 45° angle to the feed path 30. Positioning theantenna-couplers at different angles or orientations to the feed pathenables the array to communicate with a greater variety of media units.More specifically, in many applications the transponders 26 aregenerally parallel to the width of the media units 24, such that thetransponders 26 are generally perpendicular to the feed path 30, asshown in FIG. 4. However, in other applications the transponders 26 maybe angled across the media unit 24. For example, and as shown in FIG. 5,the transponders 26 may be positioned diagonally across the media unit24, such that the transponders 26 are generally at a 45° angle to thefeed path 30. An array with antenna-couplers at different orientationsmay adjust to the different orientations of the transponders on themedia units, by activating the antenna-couplers that share a similarorientation to the feed path as the transponders. Perpendicular and 45°degree orientations are only two examples of the various orientationsthat may be used within the present invention. The array may includeantenna-couplers with any orientation (e.g., 0° through 90°). It shouldbe understood that the array may include more than two antenna-couplersand more than two antenna-coupler orientations. Also, it should beunderstood that the type of antenna-couplers within the array may vary.For example, the array may include any type of stripline antenna-coupleror microstrip antenna-coupler.

Further, the present invention has been disclosed primarily in terms ofan antenna-coupler configured to broadcast primarily in the near field.However, it must be understood that the enclosure describe herein fordirecting antenna antenna-coupler signals is not restricted to nearfield antenna-couplers. It is contemplated that any type ofantenna-coupler could be encased in the enclosure to thereby direct thefields of the antenna-coupler to the open end or ends of the enclosure.

FIG. 3 illustrates an embodiment of the enclosure where the three sidesof the dielectric substrates and the ground planes are interconnected byvias, such that the fields of the antenna-coupler are directed out ofthe fourth and active side. It must be understood that this is only anexemplary configuration. Many configurations of the enclosure may beemployed to provide the desired field emission profile. Any patterncould be created by varying the portions of the sides or edges that areinterconnected. For example, portions of the fourth sides could also beenclosed to further direct the field emissions. In particular, the endportions of the fourth sides of the ground planes could beinterconnected to direct field emissions from a center portion of thefourth side of the enclosure. Oppositely, the center portion of thefourth side could be interconnected to direct the fields from the endportions of the fourth sides. Other examples come to mind. For example,open portions could be configured along any of the edges to give desiredfield emissions.

FIGS. 3, 6A and 6B illustrate sandwich type arrangements where theconductive strip or strips are sandwiched between two ground planes suchthat the fields are emitted from the sides of the antenna-coupler. Theground planes can be configured in any orientation to allowed fieldemissions from any side of the antenna-coupler. For example, groundplanes could create a tray for the antenna-coupler having a bottomformed by a first ground plane and a side wall extending around theperimeter of the bottom and formed by additional ground planes. Amicrostrip could be located in the tray such that fields emitting fromthe microstrip are encourage to propagate through a top surface of theantenna-coupler defined by an open top of the tray.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

That which is claimed:
 1. A coupler array for an RFID enabled systemhaving a media conveyance system configured to transport media unitsthat each include at least one transponder along a feed path in a feeddirection, the coupler array comprising: a plurality of couplers fortransmitting signals to one or more transponders in the feed path,wherein the plurality of couplers includes a first coupler located at afirst position relative to the feed path and a second coupler located ata second position relative to the feed path, the first position is at adifferent location than the second position.
 2. The coupler array ofclaim 1 further comprising at least a third coupler at a third positionrelative to the feed path, the third position is at a different locationthan the first position and the second position.
 3. The coupler array ofclaim 1, wherein the first coupler has a first orientation and thesecond coupler has a second orientation.
 4. The coupler array of claim4, wherein at least one of the first orientation and the secondorientation is parallel to the feed direction of the feed path.
 5. Thecoupler array of claim 4, wherein the first orientation is rotated at a45° angel relative to the second orientation.
 6. The coupler array ofclaim 4, wherein the first orientation is rotated at a 90° angelrelative to the second orientation.
 7. The coupler array of claim 4,wherein each of the first orientation and the second orientation is atan angle between 0° and 90° relative to the feed direction of the feedpath.
 8. The coupler array of claim 1, wherein the plurality of couplersincludes at least one stripline coupler.
 9. The coupler array of claim1, wherein the plurality of couplers includes at least one microstripcoupler
 10. The coupler array of claim 1, wherein each of the pluralityof couplers is selectively activated to communicate with a targetedtransponder.
 11. The coupler array of claim 1, wherein the first coupleris configured to communicate with a first transponder in a first mediaunit of the media units and the second coupler is configured tocommunicate with a second transponder in a second media unit of themedia units, the first transponder and second transponder havingdifferent orientations relative to the feed direction of the feed path.12. The coupler array of claim 1, wherein at least one coupler isselectively activated based on an orientation of a targeted transponder.13. The coupler array of claim 1, wherein at least one coupler of theplurality of couplers is activated to communicate with a targetedtransponder having a similar orientation to the feed path as thecoupler.
 14. A printer comprising: a media conveyance system configuredto transport media units that each include at least one transponderalong a feed path in a feed direction; and a coupler array comprising: aplurality of couplers for transmitting signals to the transponders inthe feed path, wherein the plurality of couplers includes a firstcoupler located at a first position relative to the feed path and asecond coupler located at a second position relative to the feed path,the first position is different than the second position.
 15. Theprinter of claim 14 further comprising a third coupler at a thirdposition relative to the feed path that is different than the firstposition and the second position.
 16. The printer of claim 14, whereinthe first coupler has a first orientation and the second coupler has asecond orientation, and at least one of the first orientation and thesecond orientation is parallel to the feed direction of the feed path.17. The printer of claim 14, wherein each of the plurality of couplersis selectively activated to communicate with a targeted transponder. 18.The printer of claim 14, wherein the first coupler is configured tocommunicate with a first transponder in a first media unit of the mediaunits and the second coupler is configured to communicate with a secondtransponder in a second media unit of the media units, the firsttransponder and second transponder having different orientationsrelative to the feed direction of the feed path.
 19. The printer ofclaim 14, wherein at least one coupler is selectively activated based onan orientation of a targeted transponder.
 20. The printer of claim 14further comprising a printhead configured to print indicia onto themedia units.